The spectral sensitizing technique of adding a certain sensitizing dye to a silver halide photographic emulsion to expand its light-sensitive wavelength region to the longer wavelength side is well known and employed for preparing silver halide photographic emulsions.
The degree of spectral sensitization is influenced by the chemical structure of the sensitizing dye, properties of the emulsion (for example, composition of silver halides, crystal habit, crystal form, silver ion concentration, hydrogen ion concentration, etc.), and the like.
This spectral sensitivity is also influenced by photographic additives copresent in the emulsion, such as a stabilizer, an antifoggant, a coating aid, a flocculating agent, a color coupler, etc.
p-Phenylenediamine type color couplers as represented by formula (II) to be shown hereinafter are known to produce cyan dyes having excellent resistance against fading upon heating in dark room. However, the use of the color coupler sometimes fails to fully remove desensitization due to mutual action with conventional cyanine dyes having one sulfoalkyl group. With cyanine dyes having two sulfoalkyl groups, desensitization is removed, but such cyanine dyes cause an increased sensitization by diffusion into another layer or layers (with light-sensitive materials having at least two layers with spectral sensitivites in different light-sensitive wavelength regions, such as color photographic light-sensitive materials, diffusion of a dye into other layer means unfavorable sensitization with the dye diffused into the other layer, hereinafter this phenomenon is called diffusion sensitization) particularly under high humidity, which is a serious problem in practical use. Thus, it has been a technically important subject to prevent this sensitization by diffusion.